Directional mobile ad-hoc networks use directional antennas to communicate between nodes. A directional antenna is one that sends and receives signals in a limited direction. When compared to omnidirectional antennas, which send and receive signals in every direction, directional antennas typically provide higher throughput rates and stronger signals for a given power output level, thereby increasing the distance a signal can be transmitted. Directional antennas may also decrease the time needed for a signal to pass through the network because fewer intermediate nodes are required to handle the signal. However, directional antennas are not well suited for use in situations where directional links can become blocked by terrain or urban obstacles. In a mobile wireless network, blockages can occur at any time because the nodes are capable of moving behind or under any of a variety of signal-blocking obstacles. Network maintenance information, such as node location and transmission availability, can be compromised by a blocked directional transmission. A network using directional transmissions must be able to detect and re-route a message around any such signal-blocking obstacles. Because nodes in a mobile network are capable of movement relative to each other, it would also be important to periodically re-evaluate the effects of signal-blocking obstacles on directional transmissions.
It is therefore an object of the invention to mitigate the effects of terrain and other signal blocking obstacles on directional signals in a mobile ad-hoc network.
It is another object of the invention to prevent loss of network maintenance information, such as node location and transmission availability, because of an obstructed directional transmission.
It is still another object of the invention to periodically re-evaluate blocked directional transmission paths to see if the paths can once again be used.
A feature of the invention is a network using directional transmissions to communicate messages between nodes, and using omnidirectional transmissions to transmit and receive network maintenance information.
Another feature of the invention is a protocol that transmits messages to a proxy node using directional transmissions when a directional transmission route to an intended target node is blocked or otherwise unavailable.
An advantage of the invention is that operation of the network is not dependent on the quality of directional transmission paths.
Another advantage is that directional transmissions can be effectively used in a mobile ad-hoc network.